1. Field of the Invention
This invention relates to gelled liquid hydrocarbon fluids and methods of their use and preparation.
2. Description of the Prior Art
In order to maximize the amount of oil derived from an oil well a process known as hydraulic pressure stimulation or, more commonly, subterranean formation fracturing is often employed. Generally, a fluid is pumped under high pressure down the wellbore through a steel pipe having small perforations in order to create or perpetuate cracks in the adjacent rock. The fluid employed must be able withstand exceptionally high shear forces. Gelled liquids, particularly gelled hydrocarbons, are often employed. In gelling the hydrocarbon on-site it is also preferred that gellation occur as quickly as possible. In addition, delayed gel breakers are used to cause the fracturing fluid to revert back to a thin fluid.
High viscosity gelled hydrocarbon containing a proppant material such as sand is used in this stimulation process. Polyvalent metal salts of phosphoric acid esters have been used to gel the hydrocarbon materials for this process. References include U.S. Pat. No. 4,622,155 issued to Harris and U.S. Pat. No. 5,846,915 issued to Smith on this process. Polyvalent metal ions include ferric or aluminum ion in these references.
Rapid gellation of hydrocarbon liquids is also required when tanks or vessels containing such liquids are damaged during transit to avoid or reduce spillage and the resultant damage to the environment. A variety of other applications exist which require the rapid gellation of hydrocarbon liquids. Therefore, several means for gelling hydrocarbon liquids are disclosed in the prior art.
U.S. Pat. No. 5,417,287 to Smith et al. is directed to a method for fracturing a subterranean formation which involves adding to a hydrocarbon liquid (a) an organic phosphate of the formula HPO4RR′ where R is an alkyl or alkaryl group having from 6 to 18 carbon atoms and R′ is hydrogen or an aryl, alkaryl, or alkyl group having from 1 to 18 carbon atoms; and (b) a ferric salt.
European Patent Application No. 551021A1 to McCabe et al. is directed to gelling a hydrocarbon liquid by adding thereto an at least partially neutralized alkyl orthophosphate acid ester, a C8-C18 surface active amine and a C2-C4 monohydric alcohol. The surface active amine employed includes alkyl and alkanol amines having from about 8-18 carbon atoms, N-heterocyclic amines, alkyl substituted derivatives of such heterocyclics and mixtures thereof. Amines having more than one nitrogen group are preferred and imidazoline such as that prepared from the reaction of a tall oil fatty acid with diethylenetriamine is most preferred.
U.S. Pat. No. 4,316,810 to Burnham is directed to a fracturing composition which is an aluminum salt of an oxaalkyl phosphate in an oil base liquid. Surface active agents are not disclosed.
U.S. Pat. No. 4,153,649 to Griffin is directed to the reaction product of a hydroxy ether and a pentavalent phosphorus compound and an alcohol. The hydroxy ether has the formula ROR1OH wherein R is a C1 to C6 alkyl group, R1 is a C2 or C3 alkylene group and the total carbon atoms of R1 and R range from 3 to about 8. The disclosed reaction product may be employed in the gelling of hydrocarbon liquids when used with a compound containing a multivalent metal cation.
U.S. Pat. No. 5,271,464 to McCabe is directed to a method of plugging or sealing a subterranean formation by introducing a rapidly gelling hydrocarbon thereto. To the hydrocarbon is added a first component which is an at least partially neutralized alkyl orthophosphate ester and a second component which is the reaction product of an aqueous source of aluminum or ferric ions and a C8-C18 surface active amine in the presence of a water miscible organic solvent. The surface active amine is as defined above for European Pat. Application No. 551021A1, also to McCabe. The water miscible organic solvent is generally a monohydric alcohol.
U.S. Pat. No. 3,494,949 to Monroe et al. is directed to an additive for improving the viscosity of motor oils which is generally an aluminum salt of an alkyl orthophosphate.
U.S. Pat. No. 2,983,678 to Pellegrini et al. is directed to an additive for lubricating oils which is generally a rare earth metal salt of a diester phosphate.
U.S. Pat. No. 6,004,908 and U.S. Pat. No. 6,147,034 are directed to a novel gel compositions for improved performance during fracturing.
In an article published at the Canadian International Petroleum Conference Petroleum Society by Taylor, et. al. on Jun. 8-10, 2004 entitled “Refinery Plugging by Residual Oil Gellant Chemicals in Crude: Understanding and Preventing the Problem through New Oil Gellant Chemistry” the role of tray plugging of the refinery distillation trays from the decomposition/volatile products of the phosphoric acid ester gelling additive was clearly detailed. This plugging causes down time at the refinery distillation facility leading to much higher costs and poorer quality.
Distillation trays in the temperature range of 230 to 290° C. produced the majority of volatile phosphorus compounds that condensed out of the gas phase and caused plugging of the holes in the trays.
Plugging of trays reduces the efficiency of distillation towers. In fact, if plugging becomes severe enough, it becomes necessary to shut down the refinery to clean the towers. Unscheduled refinery shutdowns can be extremely costly to refiners. It is also possible that phosphorus may still be present in some distillate streams such as the jet fuel draw.
U.S. Pat. Nos. 6,511,944 and 6,544,934 disclosed improved methods for fracturing subterranean formations using gelled liquid hydrocarbons which comprised the following steps: An improved gelled liquid hydrocarbon fracturing fluid is prepared comprised of a hydrocarbon liquid, a gelling agent comprised of a ferric iron or aluminum polyvalent metal salt of a phosphonic acid ester, a proppant material, water and an amount of a delayed gel breaker effective to break the gelled hydrocarbon fracturing fluid. The phosphoric acid ester utilized in the gelling agent which minimizes volatile phosphorus in refinery distillation towers has the formula
wherein R is an alkyl group having from about 8 to about 24 carbon atoms and R′ is an alkyl group having from about 1 to about 4 carbon atoms. After the gelled liquid hydrocarbon fracturing fluid is prepared, the subterranean formation to be fractured is contacted with the gelled liquid hydrocarbon fracturing fluid under conditions effective to create at least one fracture in the subterranean formation.
U.S. Pat. No. 6,511,944 above disclosed that the phosphonic acid ester used in their invention must have an R equal to tetradecyl when R′ is methyl to significantly reduce volatile emissions. This methyl tetradecyl product is not commercially available and would be expected to be expensive if made commercially available. While a variety of systems are available for gelling hydrocarbon liquids for the applications discussed above, there exists a clear need in the art for a means of improving the known phosphorous gelling agent systems to include those that are readily available and low cost, but also have low volatility are not subject to decomposition under oil drilling and refinery conditions.